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Polyurethane foam insulation

Polyurethane foam is very effective, but must be installed carefully to prevent toxic off-gassing.

What is polyurethane foam?

Polyurethane is a commonly used material for foam, and combines the best qualities of plastics and rubber. It's often used to create the padding in car upholstery and seating, as well as in cushions for furniture.

Where it comes to insulation though, it can be put to use in two separate ways – as rigid foam panels, or as a spray foam. While the panels act very much like batts in their installation and application, the spray foam method can be used to completely cover and seal a wall from air (and sometimes moisture), which can make for significantly higher R-values.

How does polyurethane foam insulation work?

The rigid polyurethane foam panel insulation is usually installed in sheets between the inner and outer wall - or cut to fit in between joists or wall studs in a frame like batts are.

Much like polystyrene, the bubbles trapped inside polyurethane foam make for a poor heat conductor and provide excellent thermal resistance. Spray foam effectively works in the same manner, although there are two types; open and closed cell foam.

Open cell foam relies on air to block the conduction of heat, while closed cell foam has much smaller bubbles which are not connected to each other and which are filled with a highly thermally resistant gas.

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How effective is polyurethane foam insulation?

Some of the highest recorded R-values come from the application of spray foam insulation. The additional boost comes from being able to completely seal in a wall cavity, effectively preventing any air from penetrating the building envelope. It also serves to block moisture from soaking in, and won’t allow mould to grow in it, which means it will retain its R-value for much longer than other types of insulation which are susceptible to these problems.

How much soundproofing does polyurethane foam provide?

Spray foam insulation makes for a more effective sound barrier than batts, as there aren't any small gaps for sound to pass through alongside the beams and joists. This total coverage also helps to buffer the beams so that they don’t vibrate as much, further dampening sound transmission.

Polyurethane is known to be very good at straining out mid-range frequencies (like conversation and loud music). For inner walls, using the less-dense open cell foam may be a better choice to prevent noise, but it's worth remembering that it's also much less waterproof, and will require moisture barriers. Specific Rw values will largely depend on what other materials you’re using in wall construction as these will affect the resonance capabilities of the wall as a whole.

How is polyurethane foam insulation supplied and installed?

Foam panels can be supplied in varying densities and thicknesses, depending on your requirements. It's usually placed in between the outer and inner wall, or cut to size and fit into the framework like batts. Since it is safe to handle and gives off no fumes or particles, installation is quite a simple matter and doesn't require any specialist equipment.

Spray foam, on the other hand, is an aerated mixture of two chemical components which must be mixed in accurate proportions, so this needs to be handled by a professional. Spray foam (as the name so helpfully suggests) is sprayed into wall cavities, and can inflate to 100 times its original volume. Once cured, it will expand and contract with the building, maintaining the closed gaps and stopping any air leaks. Existing walls can be retrofitted with polyurethane spray foam by drilling holes in key locations and spraying the foam into the cavities that way.

What does polyurethane foam insulation cost?

Spray foam is one of the more expensive options as far as insulation goes - in some cases it's up to 3-4 times the cost of batts. Having said that, it boasts some very high performance results in terms thermal and acoustic insulative properties, and can repay the initial investment over time with lower power bills for heating and cooling.

Special considerations

It's very important that spray foam is properly installed. If the two component chemicals are not mixed correctly, it can cause dangerous, toxic off-gassing for the course of the insulation’s life. All professional companies are aware of this possibility and numerous measures are taken to ensure a safe product. You should never try to install spray foam yourself unless you are qualified.

It's also worth considering that if you decide to change your insulation, spray foam can be difficult to remove properly from the frame of your house.